It is known that a fuel tank includes firstly a degassing circuit which enables the gas contained in the tank to escape during filling, and secondly a vent circuit to vent the major portion of the gases generated inside the tank because of the shaking caused by the vehicle while it is in motion.
In conventional manner, such a vent circuit comprises: a device for closing the circuit in the event of the tank being turned upsidedown, this device generally being constituted by a so-called "rollover valve" (ROV) whose function is to prevent liquid fuel from escaping from the tank via the gas vent circuit in the event of the vehicle rolling over; a device for preventing the tank being overfilled, also referred to by the [French] initials "ISR", and whose function is to close the vent circuit during filling to have the effect of maintaining a volume of gas inside the tank suitable for absorbing any excess pressure that might result from the liquid fuel heating or from the tank being deformed; a device for separating the liquid fuel from the gas for venting, also known by the initials "SLV" (for separate liquid/vapor) to prevent droplets of fuel from penetrating into the vent circuit; and a canister for fixing molecules of gaseous fuel present in the vented gas and for allowing only air cleared of fuel vapor to escape into the atmosphere.
The canister is a portion of the vent circuit that makes it necessary to have the "SLV" since it contains active carbon as the material for absorbing molecules of gaseous fuel, and active carbon degrades in contact with liquids.
To interconnect all those devices, it is necessary to prepare and assemble a certain number of ducts, and that implies cost which is not negligible either in terms of raw materials, since the ducts must be of sufficient strength and must be proof against hydrocarbons, so they need to be made out of materials that are expensive such as multilayer materials based on high density polyethylene or polyamide associated with a barrier-forming resin such as polyvinylidene fluoride or polyvinyl alcohol, or in terms of labor since it is difficult to automate interconnection of the devices, particularly if some of them are fixed on the vehicle and not on the tank, as is generally the case at least for the canister, which means that the interconnection ducts cannot be put into place remote from the vehicle assembly line.
In addition, in the vent circuit constituted by a series connection of the ducts and the various devices listed above, the ducts give rise to significant head losses, and that degrades venting efficiency.
Furthermore, the presence of ducts outside the tank increases the size of the tank, makes it difficult to handle while it is being installed on the vehicle, and makes it necessary to take account of constraints imposed by the immediate surroundings of the tank when in position on the vehicle, often constraining the ducts to follow paths over the tank that are lengthy and contorted.